linux-kernel - Re: [PATCH] Use term cumul-fence instead of fence in ->prop ordering example

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Message-ID: <20190730155847.GW14271@linux.ibm.com>
Date:   Tue, 30 Jul 2019 08:58:47 -0700
From:   "Paul E. McKenney" <paulmck@...ux.ibm.com>
To:     Alan Stern <stern@...land.harvard.edu>
Cc:     "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        linux-kernel@...r.kernel.org, Akira Yokosawa <akiyks@...il.com>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Daniel Lustig <dlustig@...dia.com>,
        David Howells <dhowells@...hat.com>,
        Ingo Molnar <mingo@...nel.org>,
        Jade Alglave <j.alglave@....ac.uk>, linux-arch@...r.kernel.org,
        Luc Maranget <luc.maranget@...ia.fr>,
        Nicholas Piggin <npiggin@...il.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Will Deacon <will@...nel.org>
Subject: Re: [PATCH] Use term cumul-fence instead of fence in ->prop ordering
 example

On Mon, Jul 29, 2019 at 04:41:34PM -0400, Alan Stern wrote:
> On Mon, 29 Jul 2019, Joel Fernandes (Google) wrote:
> 
> > To reduce ambiguity in the more exotic ->prop ordering example, let us
> > use the term cumul-fence instead fence for the 2 fences, so that the
> > implict ->rfe on loads/stores to Y are covered by the description.
> > 
> > Link: https://lore.kernel.org/lkml/20190729121745.GA140682@google.com
> > 
> > Suggested-by: Alan Stern <stern@...land.harvard.edu>
> > Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
> > ---
> >  tools/memory-model/Documentation/explanation.txt | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/tools/memory-model/Documentation/explanation.txt b/tools/memory-model/Documentation/explanation.txt
> > index 68caa9a976d0..634dc6db26c4 100644
> > --- a/tools/memory-model/Documentation/explanation.txt
> > +++ b/tools/memory-model/Documentation/explanation.txt
> > @@ -1302,7 +1302,7 @@ followed by an arbitrary number of cumul-fence links, ending with an
> >  rfe link.  You can concoct more exotic examples, containing more than
> >  one fence, although this quickly leads to diminishing returns in terms
> >  of complexity.  For instance, here's an example containing a coe link
> > -followed by two fences and an rfe link, utilizing the fact that
> > +followed by two cumul-fences and an rfe link, utilizing the fact that
> >  release fences are A-cumulative:
> >  
> >  	int x, y, z;
> > @@ -1334,10 +1334,10 @@ If x = 2, r0 = 1, and r2 = 1 after this code runs then there is a prop
> >  link from P0's store to its load.  This is because P0's store gets
> >  overwritten by P1's store since x = 2 at the end (a coe link), the
> >  smp_wmb() ensures that P1's store to x propagates to P2 before the
> > -store to y does (the first fence), the store to y propagates to P2
> > +store to y does (the first cumul-fence), the store to y propagates to P2
> >  before P2's load and store execute, P2's smp_store_release()
> >  guarantees that the stores to x and y both propagate to P0 before the
> > -store to z does (the second fence), and P0's load executes after the
> > +store to z does (the second cumul-fence), and P0's load executes after the
> >  store to z has propagated to P0 (an rfe link).
> >  
> >  In summary, the fact that the hb relation links memory access events
> 
> Acked-by: Alan Stern <stern@...land.harvard.edu>

Queued with Alan's ack, thank you both!

							Thanx, Paul